Data not received

On Sun 21st Feb I received an sms to say I was credited with 2GB data. I checked my balance and it was not reflecting. Up until this day I still had my data frim the previous month which I was using for wifi. The phone is off most of the time and was only used for a short period. I called Mtn 808 twice today Monday 25th and both agents insisted that I received the data and an application was left open and te data was depleted. The phone is off when not in use and I never received the data jn the first instance. The system may read that i was credited as per my sms as well however I kept checking my balance and even if something wad open when the phone was off my balance would have been updated. I assumed mtn had a problem therefore waited to check whether I would receive it. How can I pay for something that I did not receive. Your system may be showing my last months data was depleted recently instead. This is not good customer service. I have four contracts with Mtn and I am so disappointed that they cannot help. Data is expensive and one would be an idiot to finish it all in 1 go.